Abstract: Musical imagery—hearing music inside your head that isn’t playing in the environment—is a common yet complex experience. To capture the diversity of musical imagery, the present research develops a new conceptual framework consisting of five dimensions, including a distinction between initiation and management as different ways in which musical imagery can be voluntary. A dimensional approach can represent both common and unusual forms of musical imagery, and it can highlight conceptual similarities between seemingly different experiences. In an experience-sampling study, musicians and people from the university community (n = 132) were contacted throughout the day via a smartphone app and asked about their in vivo experiences with musical imagery, with an emphasis on five dimensions: valence, repetitiveness, vividness, length, and mental control. The results indicated substantial variability at both the within-person and between-person levels on each dimension—people have a wide variety of musical imagery experiences, not a few types. A within-person network model illustrated that the dimensions were internally coherent and distinct from each other. Taken together, the findings reveal rich heterogeneity in musical imagery and indicate that mental control over musical imagery is both common and multifaceted.